[Distutils] tracking requested vs dependency installs in PEP 376 metadata

[Carl Meyer]

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Ronald Oussoren wrote:
> That is, I install "SuperWebFramework==1.0" which happens to depend on
> peak-rules. I later start using peak-rules in my own simple scripts
> (without a setup.py or other explicit dependency information), and yet
> later decide to uninstall "SuperWebFramework".  If I understand the
> proposal correctly the uninstallation of "SuperWebFrameWork" would break
> my scripts.

Once again, let's distinguish this proposal to record a bit of metadata
from the behavior of a hypothetical tool using that metadata. This
proposal does not mandate any such behavior from an uninstall tool, or
suggest that it be the default behavior. Many implementation choices are
possible: to name just one possibility, the removal of "orphan" packages
could be a separate command, which might prompt before removing
anything. This proposal is merely to make available an extra bit of
relevant metadata that may be useful to some tools, under some use cases.

> I also wonder how this interacts with system package managers. The
> .egg-info directory-structure and PEP377 where explicitly structured to
> allow (for example) RPM to create the egg-info directory without having
> to know about Python's package repository (which would be needed if that
> repository were a single-file database instead of the collection of
> egg-info directories).

This concern is a general one about uninstallation, and is unrelated to
the proposal to add REQUESTED metadata. The REQUESTED proposal does not
create a centralized Python installation database, and changes nothing
about how Python package managers and system package managers interact.
FWIW, PEP 376 already addresses this concern via the "installer"
metadata, so tools can choose to only uninstall packages they installed.

Carl
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